Ceramic treating process and product produced thereby

ABSTRACT

A new ceramic treatment process and product and, more particularly, a process for forming and treating and shaping and treating of porous skeletal bodies to produce hardened dimensionally stable end products at relatively low temperatures and the resulting materials produced thereby which comprises the steps of treating a porous skeletal body by impregnating the interstices of the porous body with a compound of a metal capable of being converted to an oxide in situ at relatively low temperatures, heating the body so impregnated at temperatures well below normal vitrification to a temperature of at least 600* F. and for a period of time sufficient to convert the compound impregnated therein to an oxide and repeating the impregnation and heating steps until the desired degree of hardness is obtained. The invention further contemplates the forming of the porous body from relatively finely divided materials which may be relatively pure powders, mixtures of powders or impure powders, including additives in the form of discrete particles, fibers, fillers and the like, which powders are molded and bound together or bound together and molded with a binder which may comprise the impregnating compound or other suitable binder prior to treatment.

United States Patent [191 Church et al.

[ CERAMIC TREATING PROCESS AND PRODUCT PRODUCED THEREBY [75] Inventors: Peter K. Church, Cascade; Oliver J.

Knutson, Colorado Springs, both of C010.

[73] Assignee: Kaman Sciences Corporation,

Colorado Springs, Colo.

[ Notice: The portion of the term of this patent subsequent to Jan. 29, 1991, has been disclaimed.

[22] Filed: Feb, 15, 1973 [21] Appl. No.: 332,745

Related U.S. Application Data [60] Division of Ser. No. 694,303, Dec. 28, 1967, Pat. No. 3,789,096, which is a continuation-in-part of Ser. No. 642,704, June 1, 1967, abandoned.

[52] US. Cl 427/226; 427/243 [51] Int. Cl B44d 1/14 [58] Field of Search 117/169, 123 A, 123 B,

117/124 A, 126 AF, 169 A, 69; 106/57 [56] References Cited UNlTED STATES PATENTS 1,884,665 10/1932 Greiner 117/123 B 2,451,805 10/1948 Callinan... 117/126 AF 2,766,032 10/1956 Meister 117/123 B 2,839,424 611958 Labino 117/69 3,038,817 6/1962 Day et al. 117/69 3,165,422 6/1965 Stoughton et al.. 117/69 3,372,051 3/1968 Stalego 117/126 AF 3,379,523 4/1968 Chaklader... 106/57 3,385,915 5/1968 Hamling 106/57 1 *Dec. 9, 1975 Primary Examiner-Ralph l-lusack Assistant ExaminerStuart D. Frenkel Attorney, Agent, or Firm-Max L. Wymore [57] ABSTRACT A new ceramic treatment process and product and, more particularly, .a process for forming and treating and shaping and treating of porous skeletal bodies to produce hardened dimensionally stable end products at relatively low temperatures and the resulting materials produced thereby which comprises the steps of treating a porous skeletal body by impregnating the interstices of the porous body with a compound of a metal capable of being converted to an oxide in situ at relatively low temperatures, heating the body so impregnated at temperatures well below normal vitrification to a temperature of at least 600 F. and for a period of time sufficient to convert the compound impregnated therein to an oxide and repeating the impregnation and heating steps until the desired degree of hardness is obtained. The invention further contemplates the forming of the porous body from relatively finely divided materials which may be relatively pure powders, mixtures of powders or impure powders, including additives in the form of discrete particles, fibers, fillers and the like, which powders are molded and bound together or bound together and molded with a binder which may comprise the impregnating compound or other suitable binder prior to treatment.

55 Claims, 13 Drawing Figures U.S. Patent Dec. 9, 1975 Sheet 1 of 3 3,925,575

U.S. Patent Dec. 9, 1975 Sheet 2 of3 3,925,575

U.S. Patent Dec. 9, 1975 Sheet 3 0f?) 3,925,575

F 1GB.

CERAMIC TREATING PROCESS AND PRODUCT PRODUCED THEREBY This application is a division of Ser. No. 694,303, filed Dec. 28, 1967, for CERAMIC TREATING PRO- CESS AND PRODUCT PRODUCED THEREBY, now U.S. Pat. No. 3,789,096 issued Jan. 29, l974 which is a continuation-in-part of Ser. No. 642704, June 1, 1967, abandoned.

In Applicants previously filed application, Ser. No. 642,704 filed June 1, 1967, of which the present application is a continuation-in-part, Applicants disclosed the process of treating underfired porous partially vitrified relatively soft refractory ceramic which comprises the steps of shaping an underfired partially vitrified relatively soft refractory ceramic into a predetermined shape, impregnating the shaped ceramic with phosphoric acid and curing the impregnated ceramic at temperatures of at least 600F., but below vitrification temperatures for a time sufficient to drive out the moisture and produce a hard ceramic. Also disclosed was a process of producing a chemically hardened ceramic body which comprised the steps of providing a structure of a porous underfired partially vitrified substantially pure machinable refractory ceramic oxide, impregnating the core with a metal compound capable of being converted to an oxide and curing the impregnated core at temperatures of 600F. and above for a time sufficient to convert the impregnant to an oxide to harden the ceramic.

Ceramic materials normally undergo substantial dimensional changes during the usual firing or vitrification steps. Thus, it has heretofore been extremely difficult to produce precision parts or intricate shapes from ceramics. Precision parts had to be shaped slightly oversize before firing. After firing, the parts required further machining with diamond cutting wheels or by using lapping methods. Many intricate shapes were just not available since thin sections of parts would crack during firing.

In accordance with the invention, it has been found that underfired or so-called machinable grade refractory ceramics can be shaped while in the relatively soft state and then impregnated and heat treated to produce a ceramic having all the desirable characteristics of a vitrified ceramic without the usual change in dimensions. The process of the instant invention appears to be useful in the treatment of such refractory ceramic materials as the oxides of aluminum, beryllium, zirconium, titanium, magnesium and the like. These materials in the commercially available machinable grade are quite soft and easily broken. Also, in the soft state, they can be readily cut with carbide cutting tools, drilled, filed, sanded and otherwise formed to practically any desired shape. One such aluminum and beryllium oxide material is available from Coors Porcelain Company of Golden, Colorado. When the machinable ceramics are treated by the method of this invention, they become very hard, approximating highly vitrified ceramic and, in addition, will retain the original machined and pre treated dimensions. The treated material becomes so hard that the only practical method to do further machining is with diamond cutting wheels or by using lapping techniques.

The commercial value of the instant invention is readily seen when it is recognized that close tolerances on many intricate vitrified ceramic parts can only be obtained by machining with diamond cutting methods after firing. This is the case since there is considerable shrinkage which occurs during the firing. Also. there are many desired shapes which cannot be economically cast or molded using a high firing process. In addition. it is often not feasible to construct molding dies for small quantities of a particular part. The method of the present invention in contrast thereto permits easy machining of parts to exact tolerances and then hardening the part without change in original dimensions.

It has now been found that the hardening process may be equally applied to the hardening of non-sintered bodies. It has been found that the base refractory material can be prepared in a powdered form (such as ballmilled aluminum oxide) and simply pressed, molded, slip cast, extruded, or otherwise processed so that the base oxide particles are packed into close proximity to provide a porous body. The hardening of the non-sintered bodies is essentially the same method as applied to the porous, partially sintered materials. The hardening is accomplished by impregnating the porous body with a metal compound, which may be in solution, which compound is capable of being converted to the metal oxide in situ at a temperature below sintering temperature in the range of from about 600F. to about l500F. and heating the body to convert the compound to its oxide. The impregnation and cure cycle must be repeated at least for two cycles to provide any usable hardening. It has further been found that other finely divided materials, such as a powdered metal, oxide mixtures and the like will serve as the base material which may also contain additives such as glass or metal fibers or abrasive grains to provide special characteristics in the finished product.

It is, therefore, the principal object of this invention to provide an improved low temperature process for the forming and treating and shaping and treating of relatively soft porous bodies which avoids one or more of the disadvantages of prior art methods of producing close tolerance hardened shaped parts.

A further object of the present invention is to provide an improved low temperature process of producing hardened articles of manufacture of predetermined shapes, of predetermined characteristics and of predetermined dimensions.

Another object is to provide an improved low temperature method of producing articles of manufacture in close tolerance shapes of selected hardness, porosity and surface characteristics.

A still further object of the invention is to provide an improved process for the production of ceramic bearings capable of use with or without lubricants under unfavorable conditions.

A further object of the invention is to provide an improved process for the application of a refractory oxide coating to a substrate and/or the hardening of the oxide coating applied thereto.

A further object of the invention is to provide an improved low temperature process for the production of improved abrasive or polishing stones and grinding wheels which may include abrasive grain additives.

A further object of the invention is to provide a process for the production of a refractory ceramic oxide material having a negative temperature coefficient of electrical and heat conduction.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken with the drawings, and its scope will be pointed out in the ap- 3 pended claims.

FIGS. 1, 2 and 3 constitute a series of photographs of a pressed body of alumina powder with an increasing number of impregnation-cure cycles according to the present invention;

FIG. 4 is a photograph showing a grid at the same magnification as FIGS. 1-3;

FIG. 5 is a metallographic photograph at 20OX magnification of a pressed body of Alcoa T-6l(-325 mesh) alumina ball milled 48 hours and chemically hardened;

FIG. 6 is a 20OX metallographic photograph of a pressed body of Alcoa T-6l(-325 mesh) alumina ball milled 96 hours and chemically hardened;

FIG. 7 is a 200X metallographic photograph of a pressed body of beryllium oxide powder which has been chemically hardened;

FIG. 8 is a 200x metallographic photograph of a pressed body of chromium oxide powder which has been chemically hardened;

FIG. 9 is a 2OOX metallographic photograph of a pressed body of Alcoa T-6 l(-325 mesh) ball milled 96 hours with aluminum fibers added and chemically hardened;

FIG. 10 is a OX metallographic photograph of a refractory oxide painted on a metal substrate and chemically hardened;

FIG. 11 is a photograph of a commercial sintered grinding wheel side by side with a grinding wheel made by the process of this invention;

FIG. 12 is a 3OOX metallographic photograph of a cross section through a commercial plasma sprayed chromia coating prior to treatment according to this invention; and,

FIG. 13 is a 300X photograph of the cross section of FIG. 12 after treatment.

This invention is directed to a process and product involving new types of materials that are formed by multiple chemical impregnations of a relatively soft porous body of finely divided refractory oxide base materials, each followed by a low temperature cure to convert the impregnant to an oxide. The resulting ceramic structure formed in this manner has been shown to exhibit extreme hardness, a high compressive strength and a dimensionally stable material over a wide temperature range. In addition, a number of these new ce- 'ramic materials show an inherently small coefficient of friction coupled with a very low wear rate characteristic.

Parts can be economically fabricated of this new ma terial in a wide variety of intricate shapes and sizes. This is most easily accomplished by providing the base refractory material in a powdered form and packing the powder particles into close proximity by suitable means to provide a porous body of predetermined shape. The shaped pieces are then repeatedly chemically treated and cured at a temperature substantially below that used for normal ceramic vitrification.

One of the unique features of this chemical treatment and hardening method is that virtually no change occurs in the original dimensions of the shaped part during the hardening process. Therefore, expensive diamond machining of the finished hardened part is eliminated.

Many of these new ceramic materials will withstand repeated water quenching from IOOO F. as well as prolonged exposure to temperature extremes of 2000 F. to 300F. Mohs scale hardness is in excess of 9. normally being about equal to that of silicon carbide.

4 Rockwell hardness can be as high as A- to A-90. with associated compressive strengths in excess of 125,000 ps1.

In addition to their use for the manufacture of precision parts, many of these ceramics exhibit excellent characteristics for low friction and low wear rate bearing and seal applications; in particular, journal bearings, thrust bearings and sliding type bearings and seals. When used in this manner, lubrication may be by means of a wide variety of conventional and non-conventional lubricants. Among those successfully tested to date include: tap water, sea water, alcohol, kerose ne, polyethylene glycol, trichlorethylene, lubricating oils, silicone fluids and liquid metals. Solid lubricants have been used with good results at temperatures up to about 2000F. In addition, lightly loaded bearings have been operated for limited periods at high speed without lubrication.

Life tests of sleeve-type bearings have been and still are currently in progress. However, to date wear has been too low to obtain quantitative data, even after many months time. Rub-shoe type wear rate tests have consequently been conducted and have shown exceptionally low wear rate characteristics. For example, a ceramic shoe of this invention riding on a ceramic wheel of the same materialexhibited many times less wear than a bearing bronze shoe riding against a steel wheel using oil as the lubricating media. Also, unlike a conventional bronze-steel bearing combination, very heavy loads can be applied to many of the ceramic-toceramic material bearings without their showing any tendency toward galling, even when running with such poor lubricants as alcohol or water.

A special variation in treatment of this invention has also been found that will produce a honing or finishing material that appears to be superior in several respects to both natural and artifically produced grinding stones. For example,-one such ceramic will remove metal far more rapidly than will an Arkansas stone, while at the same time producing a finer and more highly polished finish. Another ceramic material of this invention displays a wide variation in electrical and heat conduction with relatively small changes in temperature.

The basic method employed for producing the new ceramic materials consists of chemically impregnating a porous, refractory oxide structure followed by a low temperature cure. The porous refractory acts as the skeletal framework around which the final ceramic structure is formed.

The simplest chemical hardening method consists of impregnating the shaped porous body with a solution of chromic acid. The thoroughly impregnated material is then cured in an oven with the final temperature reaching at least 600l000F. or higher. The impregnation and curing cycle is repeated at least once. With a suitable refractory base material, this simple acid treatment will produce a hard ceramic body having numer-.

ous uses.

The finely divided base material may be mixed with a binder, such askaolin and the like, before shaping or the impregnant may serve as the binder after the first cure. This also may be accomplished by impregnation of the porous structure with a water solution of a soluble metal compound convertible to an oxide and subsequently converting same to the oxide by simply elevating the temperature to the required conversion point. The metal compound is selected so that the oxide con- 5 version will normally take place at a temperature less than about 1500F.

As mentioned previously, the ceramic material is built around a porous refractory base material that functions as the skeletal structure. The types of such 5 6 The addresses of the manufacturers referred to in Table l are as follows: American Lava Corp.. Chattanooga, Tennessee; Amerisil, lnc., Hillside, New Jersey; Coors, Golden, Colorado; and, Du-Co Ceramics, Saxonburg, Pennsylvania.

TABLE I UNDERFIRED, POROUS REFRACTORY BASE MATERIALS Manufacturers Base Type Manu- Major Other Sintering Effective Mohs Material Designation facturer Oxide Oxides Temp. Porosity Hardness Remarks Alumina AHP-99 Coors 99% A1 0, 0.5% SiO 2670F. 45.7% 2-3 isostatic 0.2% CaO Pressed 0.2% MgO Alumina AP-99-L3 Coors 99% AI O 2570F. 42.4% 2-3 Extruded Alumina AP-99-ll Coors 99% A1 l700F. O-l Extruded Alumina AP-99-l2 Coors 99% A1 0; 2l30F. l Extruded Alumina AP-99-Ll Coors 99% AI O 2642"-F. Extruded Alumina AP-99-L2 Coors 99% Al o 2670F. -6 Extruded Alumina AP-99C-Ll Coors 99% A1 0; 2642F. 4-5 Cast Alumina AP-99C-l2 Coors 99% AI O 2l30F. Cast Alumina AP-99C-L3 Coors 99% M 0; 2570F. Cast Alumina AlSiMag 614 Am. Lava 96% M 0; SiO 2000F. l-2 ordered green.

(green) Corp. MgO fired for CaO min. at 2 000F.

Extruded rod Alumina AlSiMag 393 Am. Lava 90% A1 0 4-5 Corp. Alumina AlSiMag 548 Am. Lava 99.8%

Al O; Corp. Beryllia BP-96-il Coors 96% BeO l700F. 1-2 Extruded Magnesia l87E4 Du-Co 89% MgO SiO, 2000F. l-2

Ceramics Magnesia 187E77 Du-Co 96% MgO SiO 2000F. l-2

Ceramics Magnesium AlSiMag 222 Am. Lava MgO.Si0, 2-3 Silicate Corp. Silica No. 3 Porosity Amersil, 99% SiO, 2-3 Hot Pressed lnc. Zirconia l72H20 Du-Co 95% ZrO, 5% CaO l-2 Made from ZCA Ceramics Type F Coarse Grain Zirconia- (C aO stabilized) Titania AlSiMag l92 Am. Lava 98% TiO; SiO, 2000F. 2-3 Ordered Green Corp. MgO fired 20 min. (Underfired) CaO at 2000F. Alumina AP-995-L3 Coors 99.5% 2570F. Extruded Al,O Alumina AP-997-L3 Coors 99.7% 2570F. Cast Al,0; Alumina AP-94-il Coors 94% Al=0= 3.75% SiO, 33.l% 2-3 Extruded 0.9% CaO 0.75% MgO l700F. 0.5% ZrO, 0.l% rep. Alumina AP-94-l2 Coors 94% A1 0: 3.75% SiO 2l30F. 33.0% 2-3 Extruded 0.9% CaO 0.75% MgO 0.5% ZrO 0.1% up. Alumina AP-94-l2 Coors 94% M 0; 2l30F. 44.1% 2-3 isostatic (lsostatic) Pressed Alumina AP-BS-il Coors 85% Al ,0; l0% SiO, l700F. 33.4% 2-3 Extruded 2.75% M 1.25% CaO 0.75% BaO 0.25% Fe O Alumina AlSiMag 614 Am. Lava 96% A1 0, 2000F. 6-7 Too hard for (underfired) Corp. easy machining materials that are suitable for use in the present invention include various grades of alumina, titania, beryllia, magnesia, magnesium silicate and stabilized zirconia. Some materials were obtained from the manufacturer in an underfired or machinable form. In this condition, these materials were normally found to be soft enough to allow machining by conventional means, and exhibited a relatively high effective porosity (10 to to allow for subsequent chemical treatment by the process of this invention. Table 1 lists the major type designation, manufactuer, and indicated hardness, porosity and fabrication method for each of the skeletal refractory materials tested.

and zirconia materials, it is anticipated that many of the other partially sintered refractory oxides would make applicable skeletal structures for the improved ceramic material. Among these would be the oxides of Barium.

7 Calcium. Cerium, Chromium, Cobalt, Gallium, Hafnium, Lanthanum, Manganese, Nickel, Niobium, Tantalum, Thorium, Tin, Uranium, Vanadium. Yttrium and Zinc. Also, many of the complex-refractory oxides should be suitable base materials. Of the complexrefractories, only the magnesium silicate has been tested to date. Other complex-refractories that may be suitable if produced in a porous, partially sintered (underfired) form are Aluminum silicate, Aluminum titanate, Barium aluminate, Barium silicate, Barium zirconate, Beryllium aluminate, Beryllium silicate, Beryllium titanate, Beryllium zirconate, Calcium chromite, Calcium phosphate, Calcium silicate, Calcium titanate. Calcium zirconate, Cobalt aluminate, Magnesium aluminate, Magnesium chromite, Magnesium ferrite, Magnesium lanthanate, Magnesium silicate, Magnesium titanate, Magnesium zirconate, Magnesium zirconium silicate, Nickel aluminate, Potassium aluminum silicate, Strontium aluminate, Strontium phosphate, Strontium zirconate, Thorium zirconate, zinc aluminate, Zinc zirconium silicate and Zirconium silicate.

The novel process according to the invention is particularly adapted to the treating of porous, partially vitrified refractory ceramics such as the oxides of Aluminum, Barium, Beryllium, Calcium, Cerium, Chromium, Cobalt, Gallium, Hafnium, Lanthanum, Magnesium, Manganese, Nickel, Niobium, Tantalum, Thorium, Tin, Titanium, Uranium, Vanadium, Yttrium, Zinc and Zirconium and mixtures thereof. The oxides may be substantially pure or may contain or have amounts of impurities or additives, such as an oxide of a metal other than that of the body such as Cadmium, Chromium, Cobalt, Copper, Iron, Magnesium, Manganese, Nickel, Titanium and the like and/or other salts of such metals which ultimately will convert to oxides at least during the final curing step. The process of this invention also contemplates the addition of amounts of additives such as a salt of metal other than that of the body and convertible to an oxide such as the acetates, chlorides, nitrates and oxalates of Aluminum, Beryllium, Cadmium, Calcium, Cerium, Chromium, Cobalt, Copper, lron, Lanthanum, Lithium, Magnesium, Molybdenum, Nickel, Strontium, Thorium, Tin, Tungsten, Zinc and Zirconium which are added to the ceramic during treatment.

The process of this invention may comprise the forming of a partially sintered treated ceramic-into a predetermined shape or the forming thereof from a powder and a binder. It will be understood that, while precast machinable stock may be used, it is possible to precast to intricate shapes and prefire to an underfired condition before the ceramic is subjected to Applicants process. The ceramic, either stock or formed, is usually quite porous. The simplest method of chemically hardening the porousrefractory structure is with a phosphoric acid treatment; however, this precludes multiple treatments as the reaction seems to go to completion in one treatment. the ceramic is impregnated with a concentrated phosphoric acid solution, usually of concentration. The ceramic can be evacuated in a vacuum before immersion in the acid to hasten the impregnation or, as has been found to be'particularly effective, the ceramic can be heated to forrn about300 to about 600F. and then immersed in the phosphoric acid solution. The heating causes a vacuum to be produced within the voids of the ceramic and the phosphoric acid is drawn all through the ceramic upon immersion. While a considerably longer time is required, the ceramic also can be just immersed in the phosphoric acid solution for a length of time sufficient for complete impregnation. Greater uniformity is achieved by using the vacuum or heating impregnation techniques. When the part is thoroughly impregnated with phosphoric acid, it is removed from the solution, excess phosphoric acid on the surface is drained or wiped off.

Next, Applicants novel process comprises the controlled heat curing of the phosphoric acid impregnated ceramic. The heating cycle is usually started around 150F. and ends at about at least about 900F. The ceramic pieces are preferably placed in powdered asbestos, and the like, tominimize shock during the heating and cooling cycle. The powdered asbestos also serves to absorb liquid driven out of the ceramic as the temperature is raised. The excess liquid, if not absorbed, would be likely to craze the surface of the ceramic.

As pointed out, one of the unique features of the method of the invention is that virtually no dimensional changes occur in the machined piece during the hardening process. Therefore, expensive diamond-type machining of a hardened part is eliminated.

The property of physical hardness hasbeen used as the primary means of determining effects of varying the underfired base materials, chemical treatment and curing methods. Table 11 below sets forth the hardness measurements for various materials which have been given a simple phosphoric acid treatment.

TABLE ll HARDNESS MEASUREMENTS FOR'SlMPLE ACID TREATMENT Sample Base Type Major H -,PO Mohs Rockwell No. Material Designation Manufacturer Oxide impregnation Hardness Hardness Remarks 21E Alumina AP-ES-ll Coors 85% A1 0,, 85% 8-9 A-66.5 22E Alumina AP-94-ll Coors 9471 Al- O 85% 6-7 A-69.5 23E Alumina AP-94-l2 Coors 94% Al O 85% 6-7 A-7l.0 24E Alumina AP-94-IZ Coors 94% Al- O 85% 6-7 A-57.5

(isostatic) 25E Alumina AP-99--L3 Coors 9971 AI O 85% 8-9 A-7O5 20E Alumina AHP-99 Coors 99')? Ano, 8572 6-7 A-52 5 A7 Alumina AlSiMag 614 Am. Lava Corp. 96% A1 0 85% 8-9 A73 7 (undcrfired) 30E Alumina AlSiMag 393 Am. Lava Corp. 9071 Al. ,O;, 85% 8-9 Fractured 29E Alumina AlSiMag 54h Am. Lava Corp. 99.8% M 0;, 85% 6-7 Fractured 26E Bcryllia BP-Wa-ll Coors 9671 BcO 85% 6-7 Fractured a-l Magnesia lX7E-1 Du-Co Ceramics X97: MgO 85% 4-5 Fractured 6-1 Magn .ia 187E177 Du-Cu Ceramics 9671 MgO 85 1 4-5 A-37.0 Z8-E Magnesium AlSiM-ag 211 Am. Lava Corp. MgOSiO, 85%

Silicate 27-5 Silica No. Porosity Amcrsil, Inc. 9992 SiO X5 Fractured 56-T Titania A|Si.\lag I92 Am. Lava Corp. Ti()- 85% 4-5 Fractured (underfircd) Z-l Zirconia ITZHZU Du-('o Ceramics ZrO. 8-9 A54 (1 TABLE ll-continued HARDNESS MEASUREMENTS FOR SIMPLE AClD TREATMENT Sample Base Type Major H PO Mohs Rockwell No. Material Designation Manufacturer Oxide lmprcgnation Hardness Hardness Remarks 44T Alumina AlSiMag Am. Lava Corp. MgOSiO 85% 5-6 A-65.5

(2000F.) C60 Alumina AP 99C-l2 Coors 99% Al Q, 85% 146 Alumina AP-99C-Ll Coors 99% AI O,, 85% A-66.4

Several significant differences in the final product are achieved by the variation of portions of the treating process. While a pure or nearly pure ceramic material can be significantly hardened by a phosphoric acid treatment, prior multiple impregnations of the ceramic with a solution of a salt convertible to an oxide and cures converting same to the oxide will produce an increase in the hardness of the ceramic and the further phosphoric acid treatment which may be given if desired usually produces an even harder end product.

Where the ceramic material is impregnated with a high concentration of phosphoric acid and heat treated, a good bearing material is produced and two pieces of this same material will slide against one another with a low coefficient of friction. After such pieces are worn in for a short while, a shiny surface film is produced which remains shiny even at elevated temperatures. Where the more concentrated phosphoric acid is used, the resulting product is more dense with smaller unfilled pores. Where a relatively pure ceramic oxide is treated, the addition thereto of another oxide during treatment substantially increases the hardness of the finished product. While it is not completely known what occurs in the treating process, the pores of the underfired ceramic are believed to be filled or partially filled with a reaction product of the ceramic and the additive, if any, with the phosphoric acid, probably a complex metal phosphate.

Where the ceramic material such as aluminum oxide is impregnated with a high concentration of phosphoric acid having dissolved therein aluminum phosphate crystals until saturated at from 250 400F. and is then heat treated, a material is produced which cannot be polished to more than a dull finish, is quite porous and makes an excellent polishing and sharpening stone. This characteristic is also produced where the treatment with phosphoric acid is carried out with dilute acid solutions. It is believed that less reaction product is available to fill the pores, providing a more open and abrasive surface. Here again, the addition of another oxide during treatment substantially increases the hardness of the final product. The starting porous aluminum oxide grades have ranged from about 25 to about 60% effective porosity and, when subjected to a starved or dilute phosphoric acid treatment, remain quite porous which may account for the excellent polishing and sharpening characteristics of the thus treated material.

The heat treating of the phosphoric acid impregnated ceramic should be initiated at about 150F. to 350F. for a short period of time to drive out excess moisutre and then the temperature is raised in steps for a series of time intervals until the final cure is accomplished at at least 500- 600F. and preferably at at least 850- 900F. The ceramic will become quite hard at 500F. 600F., but good electrical resistivity is not achieved until the ceramic is subjected to a temperature of 850F. or higher. Temperatures above lOOOF. and as high as 3000F. have been used with good success. It is found that, once the heat treatment has been carried to above 850F., the temperature may be increased to well above the normal vitrifying temperatures (e.g. 3000F.) without producing any shrinkage or change in the original physical dimensions. Further, the high temperautures do not appear to affect the hardness of the material from that of the material heated to 850F.

While the mechanism of Applicants process is not completely understood, it is believed that aluminum phosphate may be formed and deposited in the crystal lattice structure of the aluminum oxide as well as within the voids of the porous ceramic. Further, the phosphates of the impurities and/or additives may be formed and possibly as part of the lattice structure.

As pointed out above, the ceramic materials which are chemically treated and hardened according to one embodiment of the present process display the unique characteristic of exhibiting a low coefficient of friction when sliding against themselves. The coefficient of friction between identical pieces of the material is considerably less than when used in contact with any dissimilar ceramic or metal tested to date.

Although these materials may be operated dry where they are lightly loaded for limited periods of time, the starting friction is considerably higher than when a lubricating material is present. Lubrication may be by a number of different liquids such as tap water, sea water, kerosene, trichlorethylene, lubricating oils, silicone fluids and liquid metals. Dry lubricants such as molybdenum di-sulfide, graphite, wax or the like are also suitable. It is possible also to form the lubricant in situ within the pore structure of the bearing.

The bearings can be easily and economically fabricated in a wide variety of shapes and sizes. The untreated ceramic material in the form of partially fired bars or plates is machined in size and shape using conventional high speed steel or carbide tooling. The machined pieces are then chemically treated and hardened at temperatures substantially below normal vitrification tempettures. The hardening occurs with substantially no change in dimensions, thus avoiding expensive diamond machining of the finished part.

The ceramic bearing being fairly porous may be used as the lubricant reservoir analogous to that of sintered bronze bearings. In other instances, the bearing can be operated partially or totally submerged in the lubricant or the non-rotating member can be connected to an external lubricant reservoir.

Typical bearings fabricated of ceramic according to the present invention can withstand repeated water quenching from at least lOO0F., as well as prolonged exposure to temperatures as high as 2000F. and as low as 300F. The compressive strength is on the order of about 125,000 psi or better, and the hardness on the Mohs scale is between 9l0 on the order of about A-8O A9O on the Rockwell scale.

The ceramic materials of Table l were subjected to several slightly different treatments according to this invention, which are: (l) impregnation in phosphoric acid alone; (2) one or more oxide impregnations followed by a single phosphoric acid treatment; or. (3) one or more oxide impregnations alone.

A typical phosphoric acid impregnation process according to the present invention comprises heating the ceramic piece to about 300- 600F. for about 20 minutes, the piece is then immersed in an 85% phosphoric acid solution while hot for about 40 minutes. The piece is then placed in an oven and progressively heated from 150F. to about lOOOF. over a period of about 120 minutes. The piece is then cooled to room temperature.

A typical combination salt and phosphoric acid impregnation process comprises heating the ceramic piece to about 250 450F. for about 20 minutes. The heated piece is then immersed in the salt solution for about 40 minutes. The piece is removed from the salt solution and cured progressively from 150 F. to about lOOF. over a period of 120 minutes. The previous steps can be repeated if desired. The piece is then cooled to about 600F. and immersed in an 85% phosphoric acid solution for about 40 minutes. The piece is then placed in an oven and cured over a temperature range of from 150 to about lOOO F. over a period of about 120 minutes and subsequently cooled to ambient temperature in about minutes.

Fully hardened samples were prepared according to the above treatments from the materials of Table I.

As previously stated, impurities existing in the base material appear to have an effect on the resultant hardness of the treated piece. Therefore, it was decided to artifically add refractory oxides to the porous base structure prior to treating with the phosphoric acid. This was accomplished by impregnating the refractory base material with a nitrate, chloride, acetate or other highly water soluble salt or an acid of the oxide desired, and then converting to the metal oxide by heating slowly to an elevated temperature. Following the oxide impregnation cycle (which may consist of one or more salt or acid treatments) and curing, the body was then treated with phosphoric acid.

Tables lll, IV, V and VI show the effect of added oxides to Coors alumina products AP-94-ll, AP-85-ll, AP-99-L3 and AHP-99, respectively. In these tests, three impregnations of the unsaturated salt were used (to assure ample loading" with the desired oxide), followed by the 85% phosphoric acid treatment.

It is interesting'to note that these tables show a wide variation in hardness depending on the oxide treatment. In some cases, the hardness is considerably increased over that of the same base material treated with acid only, while in others, the increase is not so marked. The hardness that is obtained with the phosphoric acid treatment only (no oxide impregnation) is listed for comparison purposes.

The Cr O treatment is of special interest in that, when used with the 99%, 94% and 85% Al O base structures. the resulting ceramic is exceptionally high in hardness as compared to all other oxide impregnations tested. The Cr O;-, may be added as a solution of a soluble salt or preferably as a concentrated solution of chromic acid. These four tables also show that the AHP-99 material (99% Al O is the poorest choice for the base structure of these four types. However, since the AP-99-L3 is also a 99% alumina composition, it must be assumed that the hardness is not a factor of the refractory purity alone, but that other factors such as difference in effective pore size is probably responsible for some or all of the noted differences.

Tables Vll, Vlll and [X Show the same type of data using aluminum oxides secured from the American Lava Corporation as their types 6 l4 (underfired), 393 and 548. These are 96%, and 99.8% A1 0 compositions, respectively.

Hardness measurements obtained with Coors 96% beryllium oxide for four different salt impregnations is shown in Table X. It is interesting that this base .material produces results about equal to the best alumina material tested (Coors AP99), indicating that refractory skeletal structures other than alumina are definite condidates for the ceramic fabrication method.

Tables XI and XII show hardness results for oxide impregnated magnesia material. While the hardness values are quite low as compared to the alumina or the beryllia, this is to'be expected since magnesia, even in its fully fired state, is not a particularly hard material (Mohs 5- /2).

Tables XIII and XlV cover AlSiMag No. 222 magnesium silicate and Amersil 99% silica, respectively. For reasons not fully understood, refractory base mate rials containing a high percentage of silica do not ap pear to respond well to the phosphoric acid hardening method. Even in these two tests, however, the chromic oxide impregnation provided noticeably better results than the other impregnations used.

Table XV lists results obtained with a partially sintered, zirconia refractory base material. This particular underfired zirconia was fabricated from a calcia stabilized but coarse grain material. It is anticipated that a fine grained zirconia, and possibly a magnesium oxide stabilized type, would provide better results. Nevertheless, the zirconia also reacts to the chemical hardening method in the same general manner as does the alumina, magnesia and beryllia and, toa lesser extent, the magnesia silicate ahd silica materials. Table XVA lists results obtained with aluminum oxide material and Table XVB lists results obtained with titanium dioxide material.

With regard to the effect of pore size, it would be noted that the AHP-99 Coors material has quite large pores, compared to the other Coors material, being on the order of less than one micron compared with 2 to 3 microns for the AHP-99 materials. It would appear that and substantially uniform in size.

TABLE [ll HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USlNG COORS AP 94-ll ALLIMTNA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 8-9, Rockwell 70.7)

Sample Oxide Salt No. Salt H PO Mohs Rockwell No. Formed lmpregnalion lmprcg. lnipregnation Hardness Hardness Cracks. Remarks I Al. Al( NO 3s 9-10 A-7 l .5 istmc 7l BcO BcCl 3x 9-10 A-7-1.4 None 5 ("a0 Cat No 3x 8-9 A55 None TABLE Ill-continued HARDNESS MEASUREMENTS FOR \ARIOL'S OXIDE IMPREGNATIONS USING COORS AP-94-ll ALUMlNA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 8-9. Rockwell 7057) Sample Oxide Salt N04 Salt H PO Mohs Rockwell No. Formed lmpregnation lmpreg. lmpregnation Hardness Hardness Cracks Remarks 3 CdO Cd( NO 3x 85% 8-9 A-63 None C-l CeO; Ce( N0 3x 85% 9-H) A-7 I I None 9 COO C0(NO3)2 3x 85% 8-9 A-74.8 None L-4 (Tr- O CrO; 3x 85% 9-l0 A-8I.5 None 7-3 CuO Cu(NO 3x 85% 9-10 A-filltl None 7 Fe O FeCI 3x 85% 8-9 A-72v5 None 7-5 La O La(NO;.) 3x 85% 8-9 A- 3v5 Yes 7-7 [J 0 LiC H 0 3x 85% 8-9 A482 Ycs l I MgO Mg(C H; O- 3x 85% 9-H) Fractured Yes D-5 MgCr o MgCrO 3x 85% 9-H) A-73.8 None 13 NiO Ni(NO 3x 85% 9-10 A-75.6 None D-l SnO SnCl 3x 85% 9-10 A-7 I 7 None l5 SrO Sr( N0 3x 85% 8-9 Fractured Yes 7-9 ThO Th( Noah 3X 85% 9-H) A-73.5 None I? TiO Ti,(C O 3x 85% 9-10 A-73.5 None 9-X W0 msiw o 3x 85% 9-10 A-72.I None Zn94 ZnO ZnCI 3x 85% 8-9 A-738 None ZrO, ZrOCI 3x 85% 9-IO A-76.I None D-3 I-A Fe O .Cr O l )FeCl 3x 85% 9-IO A-77 None l )CrO TABLE IV HARDN|;)'\ MIzASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING (TN 1R8 AP-85-II ALUMlNA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 8-9, Rockwell A-65.9)

Sample Oxide Salt No. Salt H;,PO Mohs Rockwell No Formed Impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks 8-4 A1 0, Al( N0 3x 85 8-9 A-7l None 8-2 CeO, Ce(N0;|)2 3x 85% 9-10 A-74 Yes 8-l Cr O CrO 3x 85%- 9- I 0 A-8l None 8-5 MgO Mg(C,H O-;) 3X 85% 8-9 A-66 Yes Shattered During Rockwell Test 8-6 TiO, TKCgO-l): 3X 85%. 8-9 A-68 Yes Shattered During Rockwell Test 8-3 ZrO, ZrOCI, 3x 85% 9-l0 A-72 None TABLE V HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING COORS AP-99-L3 ALUMlNA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 8-9. Rockwell A-7().5)

Sample Oxide Salt N0. Salt l'l-JO Mohs Rockwell N0. Formed Impregnation lmpreg lmpregnation Hardness Hardness Cracks Remarks L-4 CeO, Ce(NO.1) 3X 85% 8-9 A-69.I Yes Exploded in Oven L-l Cr O CrO 3x 85% 9-l0 A-80.5 None L-3 MgCr O MgCrO 3x 85% 9-10 A-7l.0 None L-2 ZrO ZrOCI 3x 85% 9- l 0 A-60. I None TABLE VI HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGN ATIONS USING COORS AHP-99 ALUMlNA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 5-6. Rockwell A-54.8)

Sample Oxide Salt No. Salt H PO Mohs Rockwell 0. Formed Impregnation lmpreg. Impregnation Hardness Hardness Cracks Remarks 2 AI,O;, Al(NO 3x 85% 8-9 A-60.() None 7-2 BeO BeCl 3x 85% 8-9 A-57.0 None 8-X BeO Be(NO3) 3x 85% 6-7 A-67.9 None 6 CaO Ca(NO l= 3x 85% 6-7 Fractured None 4 CdO Cd(N )z 3x 85% 4-5 A-55.() None C-S CeO Ce(NO 3x 85% 8-9 A-54.9 None I CoO Co(NO- )2 3x 85% 6-7 A-62v2 None K-7 (r 0 CrO; 3x 85% 9-10 A-69.2 None 7-4 CuO Cu(NOu)2 3x 85% 4-5 A-47.l None 8 Fe- -O;, FeCl; 3x 85% 8-9 A-45.2 None 7-6 Lu o La(NO;;) 2 3X 85% 8-9 A-59.(l None 7-8 Li O LiC H o- 3x 85% 5-6 A-53. I Yes I2 MgO Mg(C-,H O )-1 3x 85% 6-7 A-52v3 None K-3 MgCr O MgCrO 3x 85% 9-lO A-63v5 None 14 MO Ni(NO;,)- 3x 85% 7-8 A-59.6 None 6-X PbO Pb( NO 3x 85% 5-6 A-55l None 4-X Sh O- ShCI- 3x 85% 6-7 A-59v4 None TABLE VI-continued USING COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 5-6. Rockwell A-54.8)

Sample Oxide Salt No. Salt H PO Mohs Rockwell No. Formed Impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks D-2 SnO SnCl, 3x 85% 8-9 A-SZIO None lb SrO Sr( NO 3x 85% 8-9 A 161) None 7-9 Th0: Th(NO;,) 3x 85% 9-H) A-58.7 None 18 TiO Ti,(C O 3x 85% 8-9 A-53.3 None l0-X W0 H SiW O 3x 85% 8-9 A-69.0 None Zn-l ZnO Zn(NO 3x 857 8-9 A-48 1 None An99 ZnO ZnCl- 3x 85% 8-9 A-7Z.8 None K-S ZrO ZrOCI 3); 8571 8-9 A-6 l 7 None TABLE VII HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING ALSIMAG 6M (UNDERFIRED) ALUMINA REFRACTORY BASE MATERIAL" (Acid Treated Hardness Mohs 8-9. Rockwell A-73.7, 96% M 0 Sample Oxid Salt No. Salt H PO Mohs Rockwell N04 Formed Impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks A-l l CeO Ce(NO 3x 85% 8-9 A-69.0 None Fractured During Rockwell Test A-l4 C 0: CrO 3x 85% 9-l0 A-76.0 None A-l3 C00 Co(NO;)-, 3x 85% 9-l0 A-73.0 None Fractured During Rockwell Test A-8 MgCr O MgCrO; 3x 85% 9-l0 A-65.5 None Fractured During Rockwell Test A-l2 NiO Ni(NO:,,) 3x 85% 6-7 A-72.5 None Fractured During Rockwell Test A-lO ZnO Zn(NO;,) 3x 85% 6-7 A73 3 None A-9 ZIO ZroCl- 3x 857: 9-10 A-68,0 None Fractured During Rockwell Test Fired at 2000F.

TABLE VIII HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING ALSIMAG 393 ALUMINA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 8-9. Rockwell A-N.M.. 90% A1 0 Sample Oxide Salt No. Salt H PO Mohs Rockwell No. Formed impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks A-4 Cr O CrO: 3x 85% P 9-l0 A-77.0 None A-S MgCr o MgCrO 3x 85% P 9-l0 Shattered None A-6 ZrO ZrOCl, 3x 85% P 8-9 A-68.5 None TABLE IX HARDNESS MEASUREMENTSFOR VARIOUS OXIDE IMPREGNATIONS USING ALSIMAG 548 ALUMINA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 6-7, Rockwell A-N.M.; 99.8% M 0 Sample Oxide Salt No. Salt H PO. Mohs Rockwell No. Formed Impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks A-l C r 0 C [03 3 x 85% 8-9 Fractu red None A-2 MgCr O. MgCrO 3x 85% 8-9 Fractured None A-3 ZrO ZrOCl, 3x 85% 8-9 A-76.4 None TABLE X HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING COORS BP-96-ll BERYLLIA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 6-7. Rockwell A-NAM.)

Sample Oxide Salt No. Salt H;.PO Mohs Rockwell Not Formed Impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks B-l A1 0 Al( N0 3x 85% 8-9 A-74 None 8-2 C110 CrO 3x 85% 9-l0 A-8l None Shattered in Rockwell Testing B-4 MgCrO; MgCrO 3x 85% 9-10 A-7l None B-3 ZrO- ZrOCl; 3x 85% 9-10 A-75 None Shattered in Rockwell Testing TABLE XI HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING DU-CO 89% MAGNESIA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 4-5. Rockwell Fractured) Sample Oxide Salt No Salt H 1 0 Mohs Rockwell No. Formed Impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks 9-4 AI O AI(NO;) 3x 85% 4-5 Fractured None 9-2 Cr O CrO; 3x 85% 8-9 Fractured None 9-3 lvlgCr O MgCrO 3x 85% 8-9 A-5l.5 None 9-6 TlO Ti (C O 3x 85% NM. NM. MgO Base Disintegrated 9-5 2:0 ZrOCl 3x 85% NM. NM. MgO Base Disintegrated TABLE XII HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING DU-CO 96% MAGNESIA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 4-5, Rockwell A-37.0)

Sample Oxide Salt No. Salt H;,PO Mohs Rockwell No. Formed lmpregnation Impreg. Impregnation Hardness Hardness Cracks Remarks 6-4 Al O AI(NO;) 3x 85% 3-4 Fractured None 6-2 C O, CrO, 3x 85% 6-7 Fractured None 6-3 MgC O, MgCrO 3x 85% 6-7 A-44.25 None 6-6 TiO, Ti (C,O 3x 85% NM. NM. Dissolved 6-5 ZrO ZrOCI, 3x 85% NM. NM. Dissolved TABLE XIII HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING ALSIMAG 222 MAGNESlUM-SILICATE REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 2-3, Rockwell A-N.M.)

Sample Oxide Salt No. Salt H PO Mohs Rockwell No. Formed Impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks MS-I ALO, AI(NO,), 3x 85% 3-4 Fractured None MS-Z C O, CrO; 3x 85% 8-9 Fractured None MS-3 MgCr O MgCrO 3x 85% 7-8 A-4l None Shattered During Rockwell Test MS-4 ZrO, ZrOCl, 3x 85% 1-2 Fractured None TABLE XIV HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING AMERSIL NO. 3 POROSITY SILICA REFRACTORY BASE MATERIAL (Acid Treated Hardenss Mohs N.M., Rockwell A-N.M.)

Sample Oxide Salt Nor Salt H PO Mohs Rockwell Nor Formed Impregnation Irnpreg. Impregnation Hardness Hardness Cracks Remarks S-2 AI,O; AI(NO 3x 85% 4-5 Fractured None S-6 CeO, Ce(N0;) 3x 85% 4-5 Fractured None S-l Cr O CrO; 3x 85% 6-7 A-54.0 None S-3 MgO Mg(C,H;,0 )1 3x 85% 4-5 Fractu red None S-5 MgCrO MgCrO 3x 85% 6-7 Fractured None S-4 ZrO, ZrOCl, 3x 85% 4-5 Fractured None TABLE XV HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING DU-CO ZIRCONIA REFRACTORY BASE MATERIAL (Acid Treated Hardness Mohs 8-9. Rockwell A-54O) Sample Oxide Salt No. Salt H PO Mohs Rockwell No. Formed Impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks Z-4 M 0 AKNCz); 3x 85% 6-7 A-46.8 None 2-2 Cr O CrO, 3x 85% 9-l0 A-66.2 None Z-7 MgO Mg(C H;,O 3x 85% 6-7 Fractured None 2-3 MgCr O MgCrO 3x 85% 9-l0 A-S 8.0 None 2-8 Th0; Th(NOa) 3x 85% 6-7 A-55.3 None Z-6 ZnO Zn(NO;) 3x 85% 6-7 A44.7 None Z-5 ZrO ZrOCl, 3x 85% 8-9 A-60.3 None HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING ALSIMAG 6l4 96% A1 0 REFRACTORY BASE MATERIAL PARTIALLY SINTERED AT 2(l0(lF. (Acid Treated Hardness Mohs 8-9. Rockwell A73.7)

Sample Oxide Salt No. Salt H PO Mohs Rockwell No. Formed impregnation Impreg. lmpregnation Hardness Hardness Cracks Remarks T Cr O CrO;, 3x 85% 9-10 A-82.5 None 4lT ZrO ZrOCl 3x 85% 9-10 A-74.5 None 42T MgCr- O MgCrO 3x 85% 9-10 A67.5 None 43T NiO Ni(NO;,) 3x 85% 9-10 A-69.5 None 44T None 85% 5-6 A-65.6 None TABLE XVB HARDNESS MEASUREMENTS FOR VARIOUS OXIDE IMPREGNATIONS USING ALSIMAG I92 TITANIA 98% TiO REFRACTORY BASE MATERIAL PARTIALLY SINTERED AT (Acid Treated Hardness Mohs 4-5, Rockwell A-N.M.)

Sample Oxide Salt No. Salt H P O Mohs Rockwell No. Formed Impregnation lmpreg. lmpregnation Hardness Hardness Cracks Remarks SO-T Cr O CrO 3x 85% 8-9 A-77.5 None 5 l -T ZrO ZrOCl 3x 85% 8-9 A-66.0 None SZ-T BeO BC(NO3)2 3x 85% 6-7 A-69.0 None 53-T MgO Mg(C,,H;,O 3x 85% 6-7 Fractured 54-T AI O: Al(NO 3x 85% 5-6 Fractured 55-T MgCr- O MgCrO 3x 85% 9-10 A-65.0 56-T None 85% 4-5 Fractured Table XVI shows the effect of 1 through 1 1 chromic 3O oxide impregnations using Coors AP-99-L3 alumina base material, while Table XVIA shows the effect of I through 8 chromic oxide impregnations with AP-94-ll alumina base material and Table XVII'shows I through 5 impregnations with AP-94-l2 material. These tables show the definite increase in hardness with increase in number of oxide impregnations. The rate of increase in hardness is also seen to decrease as the number of impregnations increase. This would appear to follow since there is probably less and less interstitial space for the oxides with each successive treatment. Specific gravity and porosity tests bear this out.

TABLE XVI HARDNESS VARIATION WITH NUMBER OF CHROMIC OXIDE IMPREGNATIONS USING COORS AP-99-L3 ALUMINA REFRACTORY BASE MATERIAL Sample Oxide Salt No Salt H PO Mohs Rockwell No. Formed lmpregnation Impreg. lmpregnation Hardness Hardness Cracks Remarks -L Cr O CrO Ix 9-10 A-73.2 None 81-L Cr O CrO- 3 x 85% 9-10 A-80.4 None 82-L Cr O CrO 5x 85% 9-10 A-83.9 None 83-L Cr O CrO 7x 85% 9-10 A-87.6 84-L Cr O;, CIO3 9x 85% 9-l0 A-88.3 None 85-L Cr O CrO 1 1x 85% 9-10 A-88.9 None TABLE XVIA HARDNESS VARIATION WITH NUMBER OF CHROMIC OXIDE IMPREGNATIONS USING COORS AP-94-Il ALUMINA REFRACTORY BASE MATERIAL Sam ple Oxide Salt N 0. Salt H PO Mohs Rockwell No. Formed Impregnation lmpreg. Imp regnation Hardness Hardness Cracks Remark 5 L-S Cr- O; CrO Ix 85% 9-10 A-76.4 None L-9 Cr O CrO; 2x 85% 9-10 A 80.7 None 3X (fr O CrO 3x 85% 9-10 A-81.8 None 5X Cr- O CrO;, 5x 85% 9-10 A-85t0 None 6X Cr O CrO 6x 85% 9-10 A85.() None 8X Cr O: CrO 8x 85% 9-10 A-87i0 None TABLE xvn HARDNESS VARIATION WITH NUMBER OF CHROMIC OXIDE IMPREGNATIONS USING COORS AP-94-12 ALUMINA REFRACTORY BASE MATERIAL Sample Oxide Salt No. Salt H- ,PO Mohs Rockwell No. Formed Impregnation lmpregv lmpregnation Hardness Hardness Cracks Remarks L-7 C CrO 1x 85% 9-10 A-75. 8 K-8 Cr O CrO 2x 85% 9-10 A-79.6 L-4 Cr O CrO 3x 85% 9-10 A-8 I .5 L- Cr O CrO 4x 85% 9-10 A-83.9 2-S C50: CrO 5x 85% 9-10 A-86.0

3-5 Cr O: CrO- 7x 85% 9-10 A-83.0 4-5 Cr O CrO 9x 85% 9-10 A-84.0 5-S Cr O CrO; 11x 85% 9-10 A-85.0

These tables show that there is very little difference in the hardness results obtained between the AP-94-I1 the AP-99-L3 average pore size appears to be on the order of 0.6-0.7 microns.

TABLE xvnr HARDNESS VARIATION WITH NUMBER OF CHROMIC OXIDE IMPREGNATIONS USING COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL Sample Oxide Salt No. Salt H l 'O Mohs Rockwell No. Formed Impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks 0-6 Cr O CIO: 1 x 85% L-l Cr O CrO; 2x 85% 8-9 A-57.4 None O-7 C 0; CrO 3x 85% 9-10 A-69.2 None L-2 Cr- .O CrO 4x 85% 8-9 A-68.7 None O-8 Cr O CrO 5x 85% 9-10 A-73.0 None 6x 341 C1 0 cro 7x 85% 9-10 A-80.0 None 8x 4-U Cr O, CrO 9x 85% 9-10 A-76.0 None lOx 5-U C 0; CrO 1 1x 85% 9-10 A-79.0

and the AP-94-I2 materials. The difierence between these two base materials is in their sintering temperatures, respectively 1700F. and 2130F.

Table XVIII shows the results obtained with chromic oxide impregnations on Coors AI-IP-99 alumina mate- 4O rial. While the hardness increases with the number of chromic oxide impregnations, the hardness numbers obtained for a given number of treatments is much less than those obtained with chromic oxide treatment of Coors AP-99-L3 material of Table XVI. Since these lieved to be on the order of 2-3 microns average, while Tables XIX and XX show the effect on hardness for 1 through 5 impregnations of zirconium oxide into base materials of AP-94-l2 and AHP-99 alumina, respectively. Again, the AP-94 material produces greater hardness than the AHP-99 for comparable impregnations. Also, while the AP-94 material impregnated with zirconium oxide does not produce as hard an end product as does the chromic oxide impregnation, the reverse is true when considering the AHP-99 material. Again, the explanation is undoubtedly connected with differences in pore size and/or impurities in the base material.

Tables XXI and XXII show similar tests' to those just described, except that the impregnant was a concentrated solution of magnesium chromate instead of a concentrated solution of zirconyl chloride.

TABLE XIX HARDNESS VARIATIONS WITH NUMBER OF ZIRCONIUM OXIDE IMPREGNATIONS USING COORS AP-94-l2 ALUMINA REFRACTORY BASE MATERIAL Sample Oxide Salt N0. Salt H PO Mohs Rockwell No. Formed Impregnation Impreg. Imp regnation Hardness Hardness Cracks Remarks Y-l Zr0 ZrOCL, l x 8-9 A-71.9 None K-6 ZrO ZrOCl 2x 85% 8-9 A-74.6 None 5-T ZrO ZrOCI 3x 85% 9-10 A-70.0 None 4x 6-T ZrO ZrOCl 5x 85% 9-10 A-73.0 None 6x 7-T ZrO, ZrOCl 7x 85% 9-10 A-73.0 None 8 x 8-T ZrO ZrOCl- 9x 85% 9-10 A-80.5 None 1 0x 9-T ZrO ZrOCl 1 1x 85% 9-10 A-78.0 None TABLE xx HARDNESS VARIATIONS WITH NUMBERS OF ZIRCONIUM OXIDE IMPREGNATIONS USING COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL Sample Oxide Salt No. Salt H PO Mohs Rock ell No. Formed lmpregnation Impreg. impregnation Hardness Hardness Cracks Remarks Y-2 ZrO ZrCl: I x 85% 5-6 A-55.5 None Y-4 ZrO ZrCl 2x 85% 9-IO A-63.5 None K-S ZrO ZrCI 3x 85% 9-10 A-6 l 7 None Y 5 ZrO- ZnCl 4x 85% 9-10 A-7 l .6 None TABLE XXI HARDNESS VARIATION WITH NUMBER OF MAGNESIUM CHROMITE IMPREGNATIONS USING COORS AP-94-l2 ALUMINA REFRACTORY BASE MATERIAL Sample Oxide Salt No. Salt H -,PO Mohs Rockwell No. Formed Impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks M-l MgCr- ,O MgCrO, Ix 85% 9- l 0 A-66 None M-2 MgCr O MgCrO 3x 85% 9-IO A-72 None M-3 MgCr O MgCrO 5x 85% 9-I0 A-7O None TABLE XXII HARDNESS VARIATION WITH NUMBER OF MAGNESIUM CHROMITE IMPREGNATIONS USING COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL Sample Oxide Salt No. Salt H PO Mohs Rockwell No. Formed Impregnation Impreg. Impregnation Hardness- Hardness Cracks Remarks M-4 MgCgO, MgCrO l x 85% 6-7 A-SO None M-S MgCr,O MgCiO 3x 85% 9-l0 A-53 None M-6 MgCr,O MgCrO 5x 85% 9-l0 A-6l None the impregnant. TabIeXXVII is again forthe AP-94 base material but using a 1:1 mixture of concentrated ferric chloride solution and chromic acid as the impregnating solution to form what appears to be a ferric chromite when cured.

using a concentrated siIico-tungstic acid solution for TABLE XXIII HARDNESS VARIATIONS WITH NUMBER OF CERIC OXIDE IMPREGNATIONS USING COORS AP-94-ll ALUMINA REFRACTORY BASE MATERIAL Sample Oxide Salt No. Salt H PO. Mohs Rockwell No. Fon'ned lmpregnation Impreg. Impregnation Hardness Hardness Cracks Remarks C-O CcO, Ce(NOfl, 2x 85% 8-9 A-68.3 None C-l CeO, Ce( NO 3x 85% 9- I 0 A-7 I. l None C-2 CeO, Ce( N0 4x 85% 9-10 A-72.9 None C-3 CeO, Ce( NO 5x 85% 9-l0 A-74.6 None C-4 CeO, Ce( N0 6x 85% 9-IO A-75.7 None TABLE XXIV HARDNESS VARIATIONS WTIH NUMBER OF CERIC OXIDE IMPREGNATIONS USING COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL Sample Oxide Salt No. Salt H PO Mohs Rockwell No. Formed Impregnation lmpregr Impregnation Hardness Hardness Cracks Remarks C-5 CeO, Ce( N0 3x 85% 8-9 A-54.9 None C-6 CeO Ce( N0 4x 85% 8-9 A-59.4 None C7 CeO, Ce( N03): 5X 85% 8-9 A-59.0 None- C-8 CeO, Ce(NOg): 6X 85% 8-9 A-60vl None TABLE XXV HARDNESS VARIATION WITH NUMBER OF COBALT OXIDE IMPREGNATIONS USING COORS AP-94-I2 ALUMINA REFRACTORY BASE MATERIAL Sample Oxide Salt No. Salt H PO Mohs Rockwell No Formed Impregnation lmpregl Impregnation Hardness Hardness Cracks Remarks 3-8 C00 Co(NO IX 85% 9-l0 A-7l.5 None 2 X 4-8 C00 CO(NO;,) 3x 85% 9-10 A-73.0 None TABLE XXV-continued HARDNESS VARIATION WITH NUMBER OF COBALT OXIDE IMPREGNATIONS USING COORS AP-94-l2 ALUMINA REFRACTORY BASE MATERIAL Sample Oxide Salt No. Salt H PO, Mohs Rockwell No. Formed lmpregnation Impregl Impregnation Hardness Hardness Cracks Remarks 4 I-T CoO Co(NO 5x 85% 9-IO A-74.5 None TABLE XXVI HARDNESS VARIATIONS WITH NUMBER OF TUNGSTIC OXIDE IMPREGNATIONS USING COORS AP 94-12 ALUMINA REFRACTORY BASE MATERIAL Sample Oxide Salt No. Salt H PO, Mohs Rockwell No. Formed Impregnation Impreg. lmpregnation Hardness Hardness Cracks Remarks l-W W I-LSiW O Ix 85% 89 A-69.0 I None Z-W W0 H.SiW 0 3x 85% 7-8 A-7 I .0 None 5-\V W0 H SiW O 4x 85% 9-l0 A-76.0 None 3-W W0 H SiW O 5x 85% 9l0 A-76.0 None 7-W WO msiw o 6x 85% 8-W W0 H SiW O 7x 85% 9-10 A-75.0 None TABLE XXVII HARDNESS VARIATIONS WITH NUMBER OF FERRIC CHROMITE IMPREGNATIONS USING COORS AP-94-I2 ALUMINA REFRACTORY BASE MATERIAL Sample Oxide Salt No. Salt HJO Mohs Rockwell No. Formed Impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks 4-A Fe,0,Cr,O l )FeCl;+ Ix 85% 6-7 A-72 None A zirconia base material has been used for tests these tests show that one phosphoric acid treatment is shown as Tables XXVIII and XXIX. These are for a equal to, or better than, more than one treatment. coarse grain, caIcia stabilized, 95% zirconia underfired Table XXXIII shows the same type of multiple acid refractory material with chromic oxide and zirconium treatment test, except that the Coors (AP-94) material oxide impregnations as shown. has been first impregnated with three chromic acid ap- TABLE XXVIII HARDNESS VARIATIONS WITH NUMBER OF CHROMIC OXIDE IMPREGNATIONS USING DU-CO, CALCIA STABILIZED, 95% ZIRCONIA BASE MATERIAL Sample Oxide Salt No. Salt H;PO Mohs Rockwell No. Formed Impregnation Impreg. Irnpregnation Hardness Hardness Cracks Remarks 20-Z C O, CrO 3x 85% 6-7 A'-69.5 None 2l-Z C130; CrO, 5x 85% 67 A-78.5 None 22-Z C130 CrO 7x 85% 6-7 A-77 None 23-Z None None None 85% 8-9 A-54 None TABLE XXIX HARDNESS VARIATIONS WITH NUMBER OF ZIRCONIUM OXIDEIMPREGNATIONS USING DU'CO, CALCIA STABILIZED. 95% ZIRCONIA BASE MATERIAL Sample Oxide Salt No. Salt H PO Mohs Rockwell No. Formed Impregnation Impreg Impregnation Hardness Hardness Cracks Remarks 23-2 ZrO ZrOCl 3x 85% 67 A- None 24-2 ZrO ZrOCI 5x 6-7 A-66 None 25-2 ZrO ZrOCI 7x 85% 67 Fractured 262 None None None 85% 8-9 A-54 None A series of multiple phosphoric acid treatments of the Coors AP-94, AP-85 and AHP-99 alumina base plications prior to the final phosphoric acid treatments. materials has been investigated. The results are shown Again, one phosphoric acid treatment appears to be in Tables XXX, XXXI and XXXII. For the most part, optimum.

TABLE XXX ML'LTIPI E ACID IMPREGNA'I IONS USING COORS AP-94-l2 ALUMINA REFRACTORY BASE MATERIAL Sample Salt 4 No. Salt H PO No, Acid Mohs Rockwell No. lmpregnation lmpreg. lmpregnation Impreg. Hardness Hardness Cracks Remarks P-I None 85% Ix 8-9 A-68.7 None P-Z None 85% 2x 25-) A-67l8 None P-3 None 85% 3x 6-7 A677 None P-4 None 42 67 I x 4-5 A64 8 Yes Fractured P-S None 42/&% 2x 6-7 A-58.7 Yes Fractured P-o None 42/&% 3x 6-7 A-58.5 None Fractured TABLE XXXI MULTIPLE ACID IMPREGNATIONS USING COORS AP-85-ll ALUMINA REFRACTORY BASE MATERIAL Sample Salt No. Salt H PO No. Acid Mohs Rockwell No. Impregnation lmpregr lmpregnation Impreg. Hardness Hardness Cracks Remarks P-7 None 85% Ix 8-9 A-6I.2 Yes P-8 None 85% 2x 9-10 A-58,5 Yes Fractured P-9 None 85% 3x 6-7 A-63.() None P- I None 42%7; Ix 4-5 A-53.7 None 7 P- I I None 42/z% 2x 6-7 Fractured Yes Fractured P- I2 None 42 A71 3x 6-7 A-67.6 Yes TABLE XXXII MULTIPLE ACID IMPREGNATIONS USING COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL Sample Salt No, Salt H;,PO No. Acid Mohs Rockwell No Impregnation Impreg. Impregnation Impreg. Hardness Hardness Cracks Remarks P-I3 None 85% P Ix 5-6 A44 2 None P-I4 None 85% P 2x 6-7 A-45.0 Yes Fractured P-IS None 85% P 3x 6-7 A-68.0 None l-R None 85% P 3x N,M. N.M. Yes Z-R None 85% P 4x N.M. N.M. Yes 3-R None 85% P 5x N.M. N.M. Yes 4-R None 85% P 6x N.M. N.M. Yes P-I6 None 42 P Ix 4-5 A-3I.7 None P-I7 None 42%7: P 2x 6-7 Fractured Yes Fractured P-I8 None 42k% P 3x (5-? A-4I.3 None TABLE XXXIII MULTIPLE ACID IMPREGNATION TEST USING COORS AP-94-I2 ALUMINA REFRACTORY BASE MATERIAL WITH CHROMIC OXIDE PRE-TREATMENT Sample Salt No. Salt H;,PO No. Acid ,'Mohs Rockwell No. Impregnation Impreg. Impregnation Impreg. Hardness Hardness Cracks Remarks I-C CrO 3x 85% Ix 9-I0 A-82.5 None Z-C CrO 3x 85% 2x 9-IO A-8I.0 None 3-C CrO- 3x 42%7c Ix 9-10 A-78. I None 4-C CrO 3x 42'/&% 2x 9- l 0 A-B I .0 None 5-C CrO 3x 42&% 3x 9-I0 A-8I 0 None phoric acid are also compared with the standard 85% strength treatment. Table XXXIV covers the AP-94 base material and Table XXXV the AI-lP-99 material.

H PO In these two tests, 95%, 90% and 75% phos- TABLE XXXIV EFFECT ON HARDNESS OF VARYING ACID CONCENTRATION USING COORS AP-94-I2 ALUMINA REFRACTORY BASE MATERIAL Sample Salt N0 Salt H PO No. Acid Mohs Rockwell No. lmprcgnation lmpregl lmpregnation lmpreg. Hardness Hardness Cracks Remarks 2 l -E None 95% IX 5-6 A63.0 None 23-E None 85% Ix 6-7 A65.0 None -E None I x 6-7 A 59.5 None 27.E CrO 3x 95% Ix 9-H) A-83.0 None ZJ-E CrO 3x Ix 9-10 A-XUS None -3 l-E CrQ. 3x 75% Ix 8-9 A4420 None 3- CrO;, 3x 42':% Ix 9-10 A-8l I) None TABLE XXXIV-continued EFFECT ON HARDNESS OF VARYING ACID CONCENTRATION USING COORS AP-94-l2 ALUMINA REFRACTORY BASE MATERIAL Sample Salt No. Salt H PO No. Acid Mohs Rockwell Nor Impregnation lmpreg. lmpregnation Impreg. Hardness Hardness Cracks Remarks L-4 CrO; 3x 85% Ix 9-10 A-SLS None TABLE XXXV EFFECT ON HARDNESS OF VARYING ACID CONCENTRATION USING COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL Sample Salt No. Salt H PO Nov Acid Mohs Rockwell No. Impregnation Impreg Impregnation Impregv Hardness Hardness Cracks Remarks -E None 95% 1x 4-5 A-46.U None 22-E None 85% Ix 6-7 A-56.0 None 24-E None 75% Ix 6-7 A46.0 None P-l6 None 42% Ix 4-5 A3 I .7 None 26-E CrO 3x 95% Ix 5-6 A-70.0 None 28-E CrO 3x 85% Ix 4-5 A-74.0 None 30-E CrO, 3x 75% Ix 4-5 A-7 I .5 None When conducting impregnation tests with various metal oxides, it was found that a marked increase in the Mohs hardness scratch number occurred in several instances, even before the final phosphoric acid treatment. It has now been found that this marked increased in hardness occurs with at least two single oxides; chromic oxide and cobalt oxide, and at least two complex oxides; magnesium chromite and iron chromite, when used in their water soluble form as impregnants for one or more of the porous alumina base materials. A fifth impregnant, silico-tungsten acid, has also been found to react in a similar manner.

Tables XXXVI and XXXVII, respectively, show the hardness measurements obtained with AP-94-ll and AHP-99 alumina base materials with multiple impregnations with chromium trioxide chromic aci which is converted to chromic oxide on curing (no final acid treatment). Table XXXVIII covers the same two base refractory materials with multiple impregnation with magnesium chromate which is converted to magnesium chromite on curing, and Table XXXIX shows the same Coors AP-94-ll alumina material, but using multiple pregnations with ferric chloride-chromic acid solution which is converted to ferric chromite on curing. Table XXXIXA shows the Coors AP-94-l 2 material with multiple silica-tungstic acid impregnations.

TABLE XXXVI HARDNESS MEASUREMENTS FOR MULTIPLE Cr O IMPREGNATIONS WITHOUT FINAL ACID TREATMENT USING COORS AP-94-I2 ALUMINA REFRACTORY BASE MATERIAL Sample Base Salt No. Salt H PO Mohs Rockwell No. Material lmpregnation Impreg. Impregnation Hardness Hardness Cracks Remarks O- I AP-94-I2 CrO; I x None 4-5 A-43.0 None O-2 AP-94-I2 CrO; 2x None 4-5 A-62.2 None O-3 AP-94-I2 CrO, 3x None 8-9 A-74.0 None O-4 AP-94-I2 CrO; 4x None 9-10 A-82.0 None 0-5 AP-94-l2 CrO 5x None 9- l 0 A-84.0 None 3-5 AP-94-I2 CrO 7x None 9-10 A-84.0 None 4-S AP-94-I2 CrO 9x None 9- I 0 A-84.S None 5-S AP-94-I2 CrO I Ix None 9-I 0 A-86.0 None TABLE XXXVII HARDNESS MEASUREMENTS FOR MULTIPLE Cr O;, IMPREGNATIONS WITHOUT FINAL ACID TREATMENT USING COORS AHP-99 ALUMINA REFRACTORY BASE MATERIAL Sample Base Salt No. Salt H;,PO Mohs Rockwell No. Material lmpregnation Impreg. Impregnation Hardness Hardness Cracks Remarks O-6 AHP-99 CrO- Ix None 3-4 Al5.2 None O-7 AHP-99 CrO 3x None 6-7 A-54r7 None O-S AHP-99 CrQ 5x None 8-9 A-69.() None 3-U AHP-99 CrO- 7x None 9-10 Ar0 None 4-U AHP-99 CrO 9x None 9-l(l A-78lO None 5-U AHP-99 CrO I Ix None 9-10 A-79.5 None TABLE XXXVIII HARDNESS MEASUREMENTS FOR MULTIPLE MAGNESIUM CHROMITE IMPREGNATIONS WITHOUT FINAL ACID TREATMENT Sample Base Salt No. Salt H PO Mohs Rockwell Nov Material Impregnution Imprcg. Impregnution Hardness Hardness Cracks M-l AP-94-l2 MgCrO Ix None 4-5 A-24.7 None M2 AP-94-I2 MgCrO 3x None 8-) A-49v 2 None M-3 AP-94-IZ MgCrO 5x None 9-10 A-63.I None M 4 AHP-99 MgCrO Ix None 3-4 A-8.7 None M5 AHP-99 MgCrO 3x None 6-7 A 288 None M-6 AHP-99 MgCrO. 5x None 8-9 A-39.0 None TABLE XXXIX HARDNESS MEASUREMENTS FOR MULTIPLE IMPREGNATIONS WITHOUT FINAL ACID TREATMENT USING COORS AP-94-ll ALUMINA REFRACTORY BASE MATERIAL TABLE XXXIXA HARDNESS MEASUREMENTS FOR MULTIPLE TUNGSTIC OXIDE IMPREGNATIONS WITHOUT FINAL ACID TREATMENT USING COORS AP 94-I2 ALUMINA REFRACTORY BASE MATERIAL Sample Base Salt No. Salt H PO Mohs Rockwell No. Material Impregnation Impreg. Impregnation Hardness Hardness Cracks Remarks I-W AP-94-I2 Hfiiw O Ix None 4-5 A-35.0 None 2-W AP-94-l2 H SiW O 3x None 7-8 Fractured None S-W AP-94-l2 H SiW 0 4x None 8--) A-75.0 None 3-W AP-94-l2 H SiW 0 5x None 8-9 A-69.5 None 8-W AP-94-I2 H SiW O 7x None 9- l0 A-74.0 None Compressive strength tests have been conducted for XLIII cover Coors AP-94-l I, AP-94-l2, AP-85-ll and several treated refractory ceramics using the ASTM 40 AP-99-L3 alumina refractory base materials, respectentative standard, Method C5 28-637. tively, with a single phosphoric acid treatment only.

The data presented in Tables XL, XLI, XLII and TABLE XL COMPRESSIVE STRENGTH MEASUREMENTS FOR COORS AP-94-Il ALUMINA REFRACTORY BASE MATERIAL USING SINGLE ACID TREATMENT ONLY Sample Salt No. Salt H PO Sample Area Compressive No, Impregnation lmpreg. Impregnation Diameter (in) Lbf Strength Remarks I None 85% .622 .303 22.7K 74.800 psi 2 None 85% .623 .304 23.2K 76,500 psi 3 None 85% .625 .306 242K 82.200 psi 4 None 85% .622 .303 I6.2K 53.500 psi 5 None 85% .622 .303 22.4K 74 000 psi Avg. 72.500 psi TABLE XLI COMPRESSIVE STRENGTH MEASUREMENTS FOR COORS AP-94-I2 ALUMINA REFRACTORY BASE MATERIAL USING SINGLE ACID TREATMENT ONLY Sample Salt No. Salt H PO Sample Area Compressive No. lmpregnation Impreg. lmpregnation Diameter (in) Lbf Strength Remarks I None 85% .622 .303 26.3K 87.000 psi 2 None 85% .623 .304 2I.8K 71.800 psi 3 None 85% .625 .306 25.7K 83.800 psi 4 None 85% .621 .302 290K 94,000 psi 5 None 85% .624 .305 220K 72.300 psi Avg. SL800 psi 

1. A METHOD OF PRODUCING A CHEMICALLY HARDENED REFRACTORY BODY WHICH COMPRISES: FORMING AN UNSINTERED POROUS BODY FROM A MASS OF FINELY DIVIDED PARTICLES, AT LEAST THE SURFACE OF SAID PARTICLES CONSISTING OF A REFRACTORY OXIDE OF AT LEAST ONE METALLIC ELEMENT HAVING A VITRICICATION TEMPERATURE IN EXCESS OF 600*F; IMPREGNATING SAID POROUS BODY WITH A SOLUTION OF A SOLUBLE COMPOUND OF A METAL SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, BERYLLIUM, SILICONM TIN AND ZIROCONIUM WHICH COMPOUND IS CAPABLE OF BEING CONVERTED TO AN OXIDE ON HEATING TO A TEMPERATURE BELOW THE VITRIFICATION TEMPERATURE OF SAID PARTICLES; DRYING AND CURING SAID IMPREGNATED BODY BY HEATING SAME TO A TEMPERATURE OF AT LEAST 600*F. BUT BELOW THE VITRIFICATION TEMPERATURE OF THE PARTICLES TO CONVERT THE METAL COMPOUND IN SITU TO THE OXIDE; AND, REPEATING THE IMPREGNATION AND HEAT CURING STEPS AT LEAST ONCE TO HARDEN AND DENSIFY THE BODY.
 2. The method of claim 1 wherein the solution is aluminum nitrate.
 3. The method of claim 1 wherein the solution is selected from the group consisting of beryllium chloride and nitrate.
 4. The method of claim 1 wherein the solution is silica tungstic acid.
 5. The method of claim 1 wherein the solution is tin chloride.
 6. The method of claim 1 wherein the solution is selected from the group consisting of zirconyl chloride and zirconium chloride.
 7. The method of claim 1 wherein at least the surface of the particles is selected from the group of refractory oxides consisting of oxides of aluminum, barium, beryllium, calcium, cerium, chromium, cobalt, copper, gallium, hafnium, iron, lanthanum, magnesium, manganese, molybdenum, nickel, niobium, silicon, tantalum, thorium, tin, titanium, tungsten, uranium, vanadium, yttrium, zinc, zirconium and mixtures thereof.
 8. The method of claim 1 wherein at least the surface of the particles is selected from the group consisting of oxides of beryllium, chromium, silicon, tin, zirconium and mixtures thereof.
 9. The method of claim 1 wherein at least the surface of the particles is of beryllium oxide.
 10. The method of claim 1 wherein at least the surface of the particles iS of silicon oxide.
 11. The method of claim 1 wherein at least the surface of the particles is tin oxide.
 12. The method of claim 1 wherein at least the surface of the particles is zirconium oxide.
 13. A method of producing a chemically hardened refractory body which comprises: forming an unsintered porous body from a mass of finely divided refractory particles; impregnating said porous body with a solution of a soluble compound of a metal selected from the group consisting of aluminum, beryllium, silicon, tin and zirconium which compound is capable of being converted to an oxide on being heated to a temperature below the vitrification temperature of said particles; drying and curing said impregnated body by heating same to a temperature of at least 600*F. but below the vitrification temperature of the particles sufficient to convert the metal compound in situ to the oxide; and, repeating the impregnation and curing steps at least once to harden and densify the body.
 14. The method of claim 13 wherein the solution is aluminum nitride.
 15. The method of claim 13 wherein the solution is selected from the group consisting of beryllium chloride and nitrate.
 16. The method of claim 13 wherein the solution is silica tungstic acid.
 17. The method of claim 13 wherein the solution is tin chloride.
 18. The method of claim 13 wherein the solution is selected from the group consisting of zirconyl chloride and zirconium chloride.
 19. The method of claim 13 wherein the particles are packed into a mold of predetermined shape at least during the initial impregnation and curing steps.
 20. The method of claim 13 wherein the particles are selected from the group consisting of oxides of aluminum, barrium, beryllium, calcium, cerium, chromium, cobalt, copper, gallium, hafnium, iron, lanthanum, magnesium, manganese, molybdenum, nickel, niobium, silicon, tantalum, thorium, tin, titanium, tungsten, uranium, vanadium, yttrium, zinc, zirconium and mixtures thereof.
 21. The method of claim 13 wherein the refractory particles are selected from the group consisting of the oxides of beryllium, chromium, silicon, tin, zirconium and mixtures thereof.
 22. The method of claim 13 wherein the refractory particles are beryllium oxide.
 23. The method of claim 13 wherein the refractory particles are silicon oxide.
 24. The method of claim 13 wherein the refractory is tin oxide.
 25. The method of claim 13 wherein the refractory is zirconium oxide.
 26. The method of claim 13 wherein the refractory is silicon carbide.
 27. The method of claim 13 wherein the refractory is chromium oxide.
 28. A method of producing a chemically hardened refractory body which comprises: providing an unsintered porous skeletal core of refractory material; impregnating said core with a solution of a metal compound which is selected from the group of compounds consisting of aluminum, beryllium, silicon, tin and zirconium compound which are capable of being converted to an oxide on being heated; drying and curing said impregnated core by heating the core to a temperature of at least 600*F. but below the vitrification temperature of the refractory material to convert the metal compound to the oxide; and, repeating the impregnation and curing steps to harden and densify the core.
 29. The method of claim 28 wherein the solution is aluminum nitrate.
 30. The method of claim 28 wherein the solution is selected from the group consisting of beryllium nitrate and chloride.
 31. The method of claim 28 wherein the solution is tin chloride.
 32. The method of claim 28 wherein the solution is silica tungstic acid.
 33. The method of claim 28 wherein the solution is selected from the group consisting of zirconyl chloride and zirconium chloride.
 34. The method of claim 28 wherein the skeletal core is of a material selected from the group consisting of oxides of aluminum, barium, beryllium, calcium, cerium, chromium, cobalt, cOpper, gallium, hafnium, iron, lanthanum, magnesium, manganese, molybdenum, nickel, niobium, silicon, tantalum, thorium, tin, titanium, tungsten, uranium, vanadium, yttrium, zinc, zirconium and mixtures thereof.
 35. The method of claim 28 wherein the skeletal core is of a material selected from the group consisting of the oxides of beryllium chromium, silicon, tin, zirconium and mixtures thereof.
 36. The method of claim 28 wherein the skeletal core is of beryllium oxide.
 37. The method of claim 28 wherein the skeletal core is silicon oxide.
 38. The method of claim 28 wherein the skeletal core is zirconium oxide.
 39. The method of claim 28 wherein the skeletal core is chromium oxide.
 40. The method of claim 28 wherein the skeletal core is silicon carbide.
 41. A method of chemically hardening a refractory coating on a substrate having an unsintered porous coating thereon of a refractory oxide having a vitrification temperature in excess of 600*F. which comprises: impregnating the porous oxide coating with a solution of a metal compound selected from the group consisting of aluminum, beryllium, silicon, tin, and zirconium which compound is capable of being converted to an oxide on heating to a temperature below the vitrification temperature of said refractory oxide; drying and curing said impregnated coating by heating same to a temperature of at least 600*F but below the vitrification temperature of the oxide but sufficient to convert the metal compound in situ to an oxide; and, repeating the impregnation and curing steps at least once to harden and densify the coating.
 42. The method of claim 41 wherein the solution is aluminum nitrate.
 43. The method of claim 41 wherein the solution is selected from the group consisting of beryllium nitrate and chloride.
 44. The method of claim 41 wherein the solution is silica tungstic acid.
 45. The method of claim 41 wherein the solution is tin chloride.
 46. The method of claim 41 wherein the solution is selected from the group consisting of zirconyl chloride and zirconium chloride.
 47. The method of claim 41 wherein the refractory oxide is selected from the group consisting of oxides of aluminum, barium, beryllium, calcium, cerium, chromium, cobalt, copper gallium, hafnium, iron, lanthanum, magnesium, manganese, molybdenum, nickel, niobium, silicon, tantalum, thorium, tin, titanium, tungsten, uranium, vanadium, yttrium, zinc, zirconium and mixtures thereof.
 48. The method of claim 41 wherein the refractory oxide is selected from the group consisting of oxides of beryllium, chromium, silicon, tin, zirconium and mixtures thereof.
 49. The method of claim 41 wherein the refractory oxide is beryllium oxide.
 50. The method of claim 41 wherein the refractory oxide is chromium oxide.
 51. The method of claim 41 wherein the refractory oxide is silicon oxide.
 52. The method of claim 41 wherein the refractory oxide is tin oxide.
 53. The method of claim 41 wherein the refractory oxide is zirconium oxide.
 54. The method of claim 41 wherein the substrate is a metal and the oxide coating is formed thereon in situ.
 55. The method of claim 54 wherein the substrate is selected from the group of metals consisting of stainless steel, molybdenum, titanium, aluminum, iron, nickel-base alloy, chromium, tungsten and copper. 